The function of SPG7 (SPG7 matrix AAA peptidase subunit, paraplegin, Ensembl gene identifier ENSG00000197912) is as follows. Catalytic component of the m-AAA protease, a protease that plays a key role in proteostasis of inner mitochondrial membrane proteins, and which is essential for axonal and neuron development (PubMed:11549317, PubMed:28396416, PubMed:31097542, PubMed:9635427). SPG7 possesses both ATPase and protease activities: the ATPase activity is required to unfold substrates, threading them into the internal proteolytic cavity for hydrolysis into small peptide fragments (By similarity). The m-AAA protease exerts a dual role in the mitochondrial inner membrane: it mediates the processing of specific regulatory proteins and ensures protein quality control by degrading misfolded polypeptides (By similarity). Mediates protein maturation of the mitochondrial ribosomal subunit MRPL32/bL32m by catalyzing the cleavage of the presequence of MRPL32/bL32m prior to assembly into the mitochondrial ribosome (By similarity). Acts as a regulator of calcium in neurons by mediating degradation of SMDT1/EMRE before its assembly with the uniporter complex, limiting the availability of SMDT1/EMRE for MCU assembly and promoting efficient assembly of gatekeeper subunits with MCU (PubMed:28396416, PubMed:31097542). Also regulates mitochondrial calcium by catalyzing degradation of MCU (PubMed:31097542). Plays a role in the formation and regulation of the mitochondrial permeability transition pore (mPTP) and its proteolytic activity is dispensable for this function (PubMed:26387735). {ECO:0000250|UniProtKB:Q3ULF4, ECO:0000250|UniProtKB:Q9Y4W6, ECO:0000269|PubMed:11549317, ECO:0000269|PubMed:26387735, ECO:0000269|PubMed:28396416, ECO:0000269|PubMed:31097542, ECO:0000269|PubMed:9635427}.